1. Technical Field of the Invention
This invention relates generally to portable electronic equipment and more particularly to controlling of the powering such equipment.
2. Description of Related Art
As is known, integrated circuits (IC) are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radio, a pager, cellular telephones, computer memory extension (commonly referred to as a thumb drive), etc. Each of these handheld devices include one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
Integrated circuits have enabled the creation of a plethora of handheld devices, however, to be “wired” in today's electronic world, a person needs to posses multiple handheld devices. For example, one may own a cellular telephone for cellular telephone service, a PDA for scheduling, address book, etc., one or more thumb drives for extended memory functionality, an MP3 player for storage and/or playback of digitally recorded music, a radio, etc. Thus, even though a single handheld device may be relatively small, carrying multiple handheld devices on one's person can become quite burdensome.
Further, power consumption of a battery supplying energy to the handheld device is of great concern for manufacturers of such devices. As is know, the more quickly the battery is consumed, the more frequently the battery needs to be replaced, which, to most users, is an irritation. Thus, manufacturers want to minimize power consumption and, when achieved, the power reduction is highlighted to differentiate one manufacturer's product from another. However, may external devices require a 3.3 volt Input/Output interface with a system on a chip IC. This relatively high voltage is not power efficient for system on a chip. Thus, most system on chips internally use 3.3-volt devices for I/Os, including high-speed, low voltage I/Os.
Therefore, it is typical of system-on-a-chips to maintain dual supplies: a higher voltage for interfacing with external devices and a lower voltage supply for powering smaller process technology transistors of the system-on-a-chip that perform intensive computations. The need for two supplies requires the system-on-a-chip to include multiple dc-dc converters or one multi-output converter. The multi-output converters can provide additional system benefits because they require only a single inductor. However, their efficiency can be limited because the larger process technology transistors must be used even on the lower voltage output because the voltage swings that occur in producing the higher voltage output would damage smaller technology transistors if used for the lower voltage output. As is further known, the Ohmic loss in a switching transistor decreases nonlinearly as the process technology shrinks for the same gate area, so it would be very advantageous to utilize the smaller technology transistors on the lower voltage output.
Therefore, a need exists for a low-loss output stage for an on-chip boost DC-DC converter that allows for increased efficiency of the lower voltage output.